Fuel supply system for large-sized two-stroke compression ignition high-pressure gas injection internal combustion engine

Abstract

To provide a fuel supply system for supplying a high-pressure gas to a large-sized two-stroke compression ignition internal combustion engine.SOLUTION: A fuel supply system comprises a feed pipe (9) for connecting an outlet of a liquefied gas storage tank (8) to an inlet (40) of a high-pressure pump, a transfer pipe (50) for connecting an outlet of the high-pressure pump to an inlet of a high-pressure evaporator (14), and a supply pipe (18) for connecting an outlet of the high-pressure evaporator to an inlet of an engine fuel injection system. The high-pressure pump comprises two or more independently-operating extremely-low temperature pump units (41, 42 and 43). Each of the pump units comprises a pump piston (62) which is slidably arranged at a pump cylinder (61), and a drive cylinder (45) having a liquid-pressure drive piston (46) for driving the pump piston.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present disclosure relates to a fuel supply system for a large, low-speed, two-stroke, uniflow compression-ignition internal combustion engine, and more particularly to a fuel supply system for a large, low-speed, two-stroke, compression-ignition internal combustion engine that supplies high-pressure gas by high-pressure injection into the internal combustion chamber of the engine. [Background technology]

[0002] Large two-stroke uniflow turbocharged compression ignition internal combustion crosshead engines are typically used as prime movers in large ship propulsion systems or power plants. Their sheer size, weight, and power output make them quite different from typical internal combustion engines and classify them as something unique.

[0003] Large two-stroke compression-ignition internal combustion engines traditionally run on liquid fuels, for example fuel oil or heavy fuel oil. However, growing environmental concerns have led to developments towards the use of alternative fuels, such as gas, methanol, coal slurry, and petroleum coke. One group of fuels that is experiencing an increasing demand are liquefied gases, in particular liquefied natural gas (LNG). Natural gas is converted to liquid form at cryogenic temperatures in liquefaction plants. The LNG is transported over long distances to its destination by specially designed cryogenic ships (LNG carriers).

[0004] An LNG carrier is provided with one or more LNG storage tanks. LNG storage tanks have the capacity to store LNG at ultra-low temperatures of -162°C (-260°F). Generally, LNG storage tanks have a double container, with the LNG inside and the outer container containing insulation. The most common tank type is the full containment tank. The size of the tank varies greatly depending on the application. Although substantially insulated, heat is continuously transferred from the outside to the LNG inside the LNG storage tank, causing vaporization of the LNG inside the LNG storage tank. If this LNG vapor is not released from the LNG storage tank, the pressure and temperature inside the LNG storage tank will continue to increase, which is unacceptable and dangerous. LNG is a cryogen and is kept in liquid form at ultra-low temperatures. If the pressure is kept constant by venting the vaporized gas from the storage tank, the temperature inside the tank will be maintained constant. This process is known as auto-refrigeration. Therefore, during transportation of LNG by LNG carriers, LNG continuously vaporizes and generates boil-off gas in the LNG storage tanks.

[0005] The boil-off gas generated in the LNG storage tanks is used to power the ship's propulsion engines or is burned in gas combustors.

[0006] When high pressure gas injection engines, for example large two-stroke compression ignition internal combustion engines, are used as marine propulsion engines for LNG carriers, high pressure cryogenic pumps are used to pump high pressure liquefied natural gas from the LNG storage tanks to the high pressure vaporizers. Typically, cryogenic pumps have two or more pump cylinders in which pump pistons are slidably arranged. Cryogenic pumps are known which use a crankshaft to drive the pump pistons. The crankshaft is driven by an electric drive motor via a belt transmission.

[0007] The pressure of the LNG delivered to the vaporizer by the high pressure cryogenic pump is regulated by the operation of an electrically driven motor and the use of a control valve, but this known control system is relatively slow and difficult to control unsteady operation, especially with relatively rapid changes in fuel demand from large two-stroke diesel engines.

[0008] LNG is a gaseous fuel at normal temperatures and pressures, which in the context of this application are 20 degrees Celsius (°C) and 1 atmosphere (atm). LNG is typically stored in vacuum-insulated containers at or near its boiling point, approximately -160°C. Cryogenic temperatures are generally any temperature below -150°C.

[0009] In the patent document 1, a fuel gas supply device is disclosed, which comprises a reciprocating piston cryogenic pump driven by a rotary hydraulic motor. The inertia of the components of the reciprocating piston cryogenic pump, such as the crankshaft and the pistons, combined with the inertia of the rotary hydraulic motor, results in a large combined inertia of the cryogenic pump assembly. As a result, a change in the supply pressure to the rotary hydraulic motor will not be immediately translated into a change in the pressure at the outlet of the reciprocating piston cryogenic pump, because the energy stored in the moving mass takes time to be converted to energy at the outlet of the pump. Therefore, the dynamic control of the pressure delivered by the reciprocating piston cryogenic pump will be hindered by this delay and will therefore be inaccurate in situations where the delivered pressure needs to be dynamically adapted.

[0010] Therefore, there is a need to provide an improved fuel delivery system for supplying high pressure gas to large two-stroke compression ignition internal combustion engines. [Prior art documents] [Patent documents]

[0011] [Patent Document 1] EP2832972 Summary of the Invention [Problem to be solved by the invention]

[0012] It is an object of the present invention to provide a fuel delivery system which overcomes or at least mitigates the above mentioned problems. [Means for solving the problem]

[0013] These and other objects are achieved by means of the features of the independent claims. Further implementation forms are evident from the dependent claims, the description and the drawings.

[0014] According to a first aspect, there is provided a fuel supply system for supplying high pressure gas to a large two-stroke compression ignition internal combustion engine. The engine is provided with a fuel injection system for injecting the supplied high pressure gas into a combustion chamber of the engine. The fuel supply system comprises a feed pipe connecting an outlet of a liquefied gas storage tank to an inlet of a high pressure pump for transferring the liquefied gas from the liquefied gas storage tank to the high pressure pump, a transfer pipe connecting an outlet of the high pressure pump to an inlet of a high pressure carburetor for transferring the high pressure liquefied gas from the high pressure pump to the high pressure carburetor, and a supply pipe connecting an outlet of the high pressure carburetor to an inlet of a fuel injection system of the engine for transferring the high pressure carburetor to a fuel injection system of the engine. The high pressure pump comprises two or more independently operating pump units, each pump unit comprising a pump piston slidably disposed in a pump cylinder and a hydraulic drive piston slidably disposed in a drive cylinder, the drive piston being coupled to the pump piston for driving the pump piston.

[0015] By providing a fuel supply system having a high-pressure pump, each of whose pump pistons is actuated by a linear hydraulic actuator, the pressure of the high-pressure liquefied gas delivered to the carburetor can be precisely controlled by controlling the pressure of the hydraulic fluid delivered to the linear actuator. This is possible because a drive system based on a hydraulic linear actuator has virtually no inertia compared to other types of drives, and the drive system based on a hydraulic linear actuator responds immediately to pressure changes in the hydraulic fluid delivered to the hydraulic linear actuator. Thus, pressure changes in the hydraulic fluid delivered to the linear actuator are immediately reflected in the pressure of the liquefied gas delivered to the carburetor. It is relatively easy and simple to control the hydraulic supply pressure. Thus, the pressure of the gas can be controlled with a significantly faster response time and less overshoot.

[0016] According to a first possible embodiment of the first aspect, the fuel supply system further comprises at least one hydraulic control valve connected to a source of high pressure hydraulic fluid and to the tank for controlling the flow of hydraulic fluid to and from the drive cylinders of the one or more pump units, the source of high pressure hydraulic fluid being preferably a source of variable and controllable pressure level.

[0017] According to a second possible embodiment of the first aspect, the drive cylinder comprises a drive chamber and a return chamber.

[0018] According to a third possible embodiment of the first aspect, the drive chamber is connected to a hydraulic control valve and the return chamber is preferably permanently connected to a source of hydraulic fluid at a pressure lower than the pressure of the source of high pressure hydraulic fluid.

[0019] According to a fourth possible embodiment of the first aspect, the drive cylinders are provided with position sensors for sensing the position of the drive piston in the associated drive cylinder.

[0020] According to a fifth possible embodiment of the first aspect, the fuel supply system further comprises an electronic control unit that receives a signal from the position sensor, and the at least one hydraulic control valve is an electronically controlled valve coupled to the electronic control unit.

[0021] According to a sixth possible embodiment of the first aspect, the electronic control unit is configured to selectively connect a drive chamber of the pump unit to a source or a tank of high pressure hydraulic fluid.

[0022] According to a seventh possible embodiment of the first aspect, the electronic control unit is configured to initiate a pump stroke of a drive piston when a pump stroke of another drive piston is nearing an end and there is a small overlap between the ending and starting pump strokes, thus achieving a substantially steady flow of LNG to the vaporizer without large pressure fluctuations.

[0023] According to an eighth possible embodiment of the first aspect, the electronic control unit is configured to take into account the power at the end of a pump stroke and the power at the start of a pump stroke in order to obtain a substantially constant flow of high pressure liquefied gas from the high pressure pump to the high pressure vaporizer.

[0024] According to a ninth possible embodiment of the first aspect, the electronic control unit is configured to determine when a pump stroke of one of the drive cylinders / units should start and when a pump stroke of any of the drive cylinders should end, so that the point at which a pump stroke starts and, in particular, where a pump stroke ends can be precisely controlled.

[0025] According to a tenth possible embodiment of the first aspect, the electronic control unit is configured to operate each of the drive cylinders substantially consecutively, preferably with a small overlap.

[0026] According to an eleventh possible embodiment of the first aspect, the electronic control unit is configured to operate the drive pistons of the remaining functioning pump units in case of failure of one of the pump units, thus providing redundancy and allowing pumping action to continue even if one of the pump units fails.

[0027] According to a twelfth possible embodiment of the first aspect, the electronic control unit is configured to operate the drive pistons of the remaining functioning pump units such that the drive cylinders of the remaining functioning pump units are operated substantially continuously, preferably with a small overlap.

[0028] According to a thirteenth possible embodiment of the first aspect, the electronic control unit is configured to adjust the position of the drive piston at which the drive chamber is decoupled from the source of high pressure hydraulic fluid in relation to the magnitude of the flow of liquefied gas from the high pressure pump to the high pressure vaporizer, so that the position at which the pump stroke reverses can be kept the same regardless of the speed and induced inertia of the pump piston and the drive piston.

[0029] According to a fourteenth possible embodiment of the first aspect, the electronic control unit is configured to adjust a position of a drive piston in a direction opposite to the direction of the drive stroke, at which a drive chamber of the associated drive piston is disconnected from the source of high pressure liquid, when the flow of liquefied gas from the high pressure pump to the high pressure vaporizer increases.

[0030] According to a fifteenth possible embodiment of the first aspect, the electronic control unit is configured to adjust a position of a drive piston in the direction of the drive stroke at which a drive chamber of an associated drive piston is disconnected from the source of high pressure liquid when the flow of liquefied gas from the high pressure pump to the high pressure vaporizer decreases.

[0031] According to a sixteenth possible embodiment of the first aspect, the electronic control unit is configured to adjust, by algorithm, planning or randomization, the positions of the drive pistons at which the drive chambers of the associated drive pistons are disconnected from the source of high pressure fluid in order to distribute the positions at which the pump pistons reverse over a stroke area of ​​the pump pistons in order to reduce wear on the pump cylinder.

[0032] According to a seventeenth possible embodiment of the first aspect, the electronic control unit is configured to control the pressure of the liquefied gas in the transfer pipe by controlling the pressure of the hydraulic fluid supplied to the drive chamber, thus realizing an effective and immediately responsive control of the pressure of the liquefied gas in the transfer pipe.

[0033] According to an eighteenth possible embodiment of the first aspect, the electronic control unit is configured to use a desired pressure of the liquefied gas in the transfer pipe in a feedforward function for controlling the pressure of the hydraulic fluid supplied to the drive chamber. By using a feedforward control of the pressure of the liquefied gas via the hydraulic pressure, a more rapid and stable control of the pressure of the liquefied gas can be achieved.

[0034] According to a nineteenth possible embodiment of the first aspect, the electronic control unit is configured to use the measured pressure of the liquefied gas in the transfer tube in a feedback function for controlling the pressure of the hydraulic fluid supplied to the drive chamber, thus allowing non-linearities and temporary variations to be accommodated by the control system.

[0035] According to a twentieth possible embodiment of the first aspect, the electronic control unit is configured to control the activation and deactivation of each drive piston independently of controlling the pressure of the hydraulic fluid supplied to the drive chamber, so that a control method for the activation of the drive pistons can be optimized by the electronic control unit independently of the pressure control.

[0036] According to a twenty-first possible embodiment of the first aspect, the electronic control unit is configured to use a signal representative of a position of the drive piston to control activation and deactivation of the drive piston.

[0037] According to a second aspect, there is provided a large two-stroke turbocharged compression ignition internal combustion engine having a high pressure gas injection system according to the first aspect and any possible embodiment thereof, and a fuel supply system.

[0038] According to a third aspect, there is provided an LNG carrier or a cargo ship having liquefied gas tanks, comprising an engine according to the second aspect.

[0039] According to a fourth aspect, there is provided a method for supplying high pressure vaporized gas to an internal combustion engine for injection of the high pressure gas into the engine, the method comprising: storing the liquefied gas in a liquefied gas storage tank; pumping the liquefied gas into a high-pressure vaporizer using a high-pressure pump; vaporizing a high pressure liquefied gas in a high pressure vaporizer; and supplying the vaporized high pressure gas to an engine. The high pressure pump includes two or more independently operable pump units, each pump unit including a pump piston slidably disposed in a pump cylinder and a hydraulic drive piston coupled to the pump piston for driving the pump piston, and the method further includes: supplying high pressure hydraulic fluid to the drive cylinders individually to drive the drive pistons individually; and controlling the pressure of the liquefied gas leaving the high pressure pump by individually controlling the pressure of the hydraulic fluid supplied to the drive cylinders.

[0040] According to a first possible embodiment of the fourth aspect, the method further comprises activating one of the drive pistons for a drive stroke and thereafter deactivating that one drive piston for a return stroke.

[0041] According to a second possible embodiment of the fourth aspect, the pump piston and the drive piston are connected to each other and move simultaneously.

[0042] According to a third possible embodiment of the fourth aspect, the method further comprises starting a pump stroke of a drive piston when a pump stroke of another drive piston is nearing an end point and there is a small overlap between the ending pump stroke and the starting pump stroke.

[0043] According to a fourth possible embodiment of the fourth aspect, the method further comprises taking into account the power at the end of a pump stroke and the power at the start of a pump stroke to obtain a substantially constant flow of high pressure liquefied gas from the high pressure pump to the high pressure vaporizer.

[0044] According to a fifth possible embodiment of the fourth aspect, the method further comprises operating each of the drive cylinders substantially consecutively, preferably with a small overlap.

[0045] These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter.

[0046] In the following detailed section of the disclosure, the invention will be explained in more detail with reference to exemplary embodiments shown in the drawings. [Brief description of the drawings]

[0047] [Figure 1] FIG. 1 is an elevational front view of a large two-stroke diesel engine according to an exemplary embodiment; [Diagram 2] Diagram of a fuel supply system that supplies high-pressure natural gas from an LNG storage tank to a large two-stroke diesel engine as shown in Figure 1. [Diagram 3] FIG. 3 is an elevational view of a high-pressure pump of the fuel injection system of FIG. [Figure 4] Diagram of the high pressure pump in Figure 3 [Diagram 5]Detailed cross-sectional view of the pump unit of the high-pressure pump in Figure 3 [Figure 6] 4 is a graph illustrating the operation of the high pressure pump of FIG. [Figure 7] 4 is a graph illustrating the operation of the high pressure pump of FIG. [Figure 8] 4 is a graph illustrating the operation of the high pressure pump of FIG. [Figure 9] FIG. 4 illustrates a control system for controlling the high pressure pump of FIG. [Figure 10] A graph illustrating the movement of the piston of the high pressure pump of FIG. 3 at various speeds. [Figure 11] A graph illustrating the movement of the piston of the high pressure pump of FIG. 3 at various speeds. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0048] In the following detailed description, a fuel supply system for a large two-stroke, slow-speed turbocharged, compression-ignition internal combustion engine having a crosshead is described with reference to an exemplary embodiment, but the internal combustion engine can also be of another type, such as two-stroke Otto, four-stroke Otto or diesel, with or without a turbocharger, with exhaust gas recirculation or selective catalytic reduction or without exhaust gas recirculation or selective catalytic reduction.

[0049] FIG. 1 shows a large slow-speed turbocharged two-stroke diesel engine with a rotating wheel and a crosshead. In this exemplary embodiment, the engine is an in-line six-cylinder. Large slow-speed turbocharged two-stroke diesel engines typically have 4 to 14 cylinders in-line and are supported on a cylinder frame supported on an engine frame 6. This engine may be used, for example, as the main engine of a ship or as a stationary engine to run a generator in a power plant. The total power output of this engine may be, for example, in the range of 1,000 to 110,000 kW.

[0050] In this exemplary embodiment, the engine is a two-stroke uniflow type compression ignition engine with scavenging ports in the lower region of the cylinders 1 and a central exhaust valve 4 in the upper part of the cylinder liner 1. Scavenging air is delivered from a scavenging air receiver 2 to the scavenging ports of the individual cylinders 1. The pistons in the cylinder liners 1 compress the scavenging air and high pressure gas fuel is injected through the fuel valves in the cylinder covers, where combustion occurs and exhaust gases are generated.

[0051] When the exhaust valve 4 opens, the exhaust gases flow through an exhaust duct associated with the cylinder 1 to an exhaust gas receiver 3 and then to the turbine of a turbocharger 5, from where they flow through an exhaust pipe to the atmosphere. The turbine of the turbocharger 5 drives a compressor that is fed with fresh air via an air inlet. The compressor delivers compressed scavenging air to a scavenging pipe that leads to the scavenging air receiver 2. The scavenging air in the scavenging pipe passes through an intercooler 7 where it is cooled.

[0052] 2 is a simplified diagram of a fuel supply system for an engine, which may be installed in a vessel, such as an LNG carrier, or a cargo vessel with liquefied gas tanks, such as a container ship with liquefied gas tanks.

[0053] The fuel supply system comprises an LNG storage tank 8 in which natural gas is stored at cryogenic temperatures. The pressure in the LNG storage tank 8 is kept relatively low and constant so that boil-off gas can be vented from the tank for use in low-pressure gas injection engines, such as boilers or spare engines on ships. The boil-off process also keeps the LNG in the storage tank at a low temperature. The liquefied gas in the storage tank 8 may be of another type than natural gas, such as ethane or methane.

[0054] A feed pipe 9 connects the outlet of the LNG storage tank 8 to the inlet of the high pressure pump 40. A low pressure feed pump 10 assists in transferring liquefied gas from the LNG storage tank 8 to the inlet of the high pressure pump 40. Alternatively, the LNG storage tank 8 can be pressurized and the low pressure feed pump 10 can be omitted. A transfer pipe 50 connects the outlet of the high pressure pump 40 to the inlet of the high pressure vaporizer 14 to transfer the high pressure liquefied gas from the high pressure pump 40 to the high pressure vaporizer 14. The high pressure pump 40 pumps the liquefied gas through the transfer pipe 50 to the high pressure vaporizer 14. The high pressure vaporizer 14 receives the high pressure liquefied gas and vaporizes the gas using a heat exchanger of the high pressure vaporizer 14. The high pressure vaporizer 14 exchanges heat between the liquefied gas and a heat exchange medium, such as glycol, circulating through a circulation circuit 15. The circulation circuit 15 includes a circulation pump 16 and a heater 17. The high pressure vapor leaves the high pressure vaporizer 14 through an outlet of the high pressure vaporizer 14 which is connected to a supply line 18 .

[0055] A supply pipe 18 connects the outlet of the high pressure carburetor 14 to the inlet of the engine's fuel injection system to allow the transfer of high pressure carburetor gas to the engine's fuel injection system. A valve arrangement 19 controls the connection between the fuel supply system and a large two-stroke diesel engine.

[0056] The high pressure pump 40 is provided with two or more pump units 41, 42, 43 (three pump units are shown in this embodiment), each pump unit 41, 42, 43 including a pump piston 62 slidably disposed in a pump cylinder 61 and a hydraulic drive piston 46 slidably disposed in a drive cylinder 45 having a drive piston 46 coupled to the pump piston 62 for driving said pump piston 62.

[0057] The pump piston 62 and the pump cylinder 61 form a cryogenic positive displacement pump. The pump piston 62 and the pump cylinder 61 form a so-called cold end of a pump unit having a pump chamber 63. The cold end is kept at a low temperature by a circulation circuit including a liquefied gas circulation supply pipe 11 and a liquefied gas circulation return pipe 12. The circulating liquefied gas serves to cool the cold ends of the pump units 41, 42, 43.

[0058] The pump cylinder 61 is connected to the drive piston of the associated pump unit 41, 42, 43 via a piston rod 49. The drive piston 46 divides the interior of the drive cylinder 45 into a drive chamber 48 and a return chamber 47.

[0059] The drive cylinder 45 is connected to a source 20 of high pressure hydraulic fluid, such as a pump or pump station, via a high pressure hydraulic fluid supply line 23. In the embodiment shown, the source 20 of high pressure hydraulic fluid includes an electric drive motor 21 driving a high pressure pump 22. The high pressure pump 22 may be, for example, a positive displacement pump, preferably a variable displacement positive displacement pump. In one embodiment, for redundancy purposes, the source of high pressure hydraulic fluid includes two high pressure hydraulic pumps 22, each driven by its own electric drive motor 21.

[0060] 3 is an elevational view of a high pressure pump 40 having three pump units 41, 42, 43, each with a pump cylinder 61, a drive cylinder 45, a control valve 24, supported by a frame 35, together with an accumulator 53 for equalizing the high pressure of the high pressure pump 40 and for equalizing the low pressure of the return chamber. The pump units 41, 42, 43 are compactly arranged on the frame 35, and the components on the frame 35 only have non-sparking components and ATEX approved electrical components, so that the unit can be installed without problems in an ATEX environment.

[0061] 4 shows the high pressure pump 40 with its pump units 41, 42, 43. Each pump unit 41, 42, 43 is connected to a source of high pressure hydraulic fluid including a variable displacement positive displacement pump 22 connected to a tank via a hydraulic fluid return line 26 and to the respective pump unit 41, 42, and 43 via a hydraulic fluid supply pipe 23. Each pump unit 41, 42, and 43 is connected to a transfer pipe 50.

[0062] Each pump unit 41, 42, 43 includes a hydraulic control valve 24 configured to selectively connect a respective drive chamber 48 via a control line 25 to a source or tank of high pressure hydraulic fluid.

[0063] Each pump unit 41, 42, 43 comprises a drive unit 44 in the form of a linear hydraulic actuator formed by a drive cylinder 45 in which a drive piston 46 is slidably arranged. The pump units are therefore mechanically independent of one another. The return chamber 47 is permanently connected to a hydraulic supply source. The hydraulic supply source comprises a hydraulic pump 30, for example a variable displacement positive displacement pump, via a return chamber supply line 31, which preferably comprises a flow restriction 33 and is coupled to an accumulator 32 for ensuring a steady supply of pressurized hydraulic fluid to the return chamber 47. Alternatively, a low pressure supply is obtained from a high pressure hydraulic system via a pressure reducing valve. In one embodiment, the pressure of the hydraulic fluid supplied to the return chamber is significantly less than the pressure of the hydraulic fluid supplied to the drive chamber 48. Alternatively, the effective pressure surface of the side of the drive piston 46 facing the return chamber 47 can be arranged to be significantly less than the effective pressure surface of the drive piston facing the drive chamber 48. In the latter case, the pressure of the hydraulic fluid in the return chamber 47 can be made substantially equal to the pressure of the hydraulic fluid supplied to the drive chamber.

[0064] Each pump unit 41, 42, 43 comprises a pump 60 in the form of a linear positive displacement pump formed by a pump cylinder 61 receiving a pump piston 62 therein to form a pump chamber 63. The pump chamber 63 is connected to the feed pipe 9 via a first one-way valve 51 which allows flow only to the pressure chamber 63. The pump chamber 63 is connected to the transfer pipe 50 via a second one-way valve 52 which allows flow only from the pressure chamber 63.

[0065] FIG. 5 is a detailed cross-sectional view of the pump units 41, 42, 43 of the high-pressure pump 40. The pump units 41, 42, 43 comprise a hydraulic linear actuator 44, which comprises a cylinder 45 in which a drive piston 46 is arranged. The drive piston 46 is connected, preferably as one piece, to a piston shaft 47. The piston rod 49 and the drive piston 46 are provided with a bore 58 for receiving a rod 57 of a position sensor 56. The signal of the position sensor 56 is sent to an electronic control unit 70. The drive piston 46 divides the interior of the drive cylinder 45 into a drive chamber 48 and a return chamber 47. In FIG. 5, the return chamber is not visible because the drive piston 46 has reached the end of its drive stroke. The drive chamber 48 is connected to the hydraulic control valve 24 via a bore 25. The return chamber 47 is permanently connected to a hydraulic supply source via a bore 31.

[0066] The piston rod 49 of the linear hydraulic actuator 44 is connected to a piston rod 62 of a cryogenic pump 60. The connection between the piston rod 49 and the piston rod 62 is established by a connector piece 54 so that the piston rod 49 and the piston rod 62 move together. The drive cylinder 45 is connected to the pump cylinder 61 by a bolted connection 55. The cryogenic pump 60 is provided with an outlet connecting the pump chamber 63 to the transfer tube 50.

[0067] FIG. 9 is a diagram illustrating a control system in the form of an electronic control unit 70 for controlling the operation of the high pressure pump 40.

[0068] An electronic control unit 70 receives a gas pressure set point 71. The gas pressure set point 71 is sent to a summing point 72. At the first summing point 72 the measured gas pressure is subtracted and the difference between the set point and the measured gas pressure is sent to a PI controller 74 which is part of a feedback control loop.

[0069] The gas pressure set point is sent to a feedforward piston ratio gain unit 78. The signal from the feedforward piston ratio gain unit 78 is compared to the signal from the PI controller 74 at a second summing point 76.

[0070] The measured gas pressure sent to the first summing point 72 is based on a measurement of the gas pressure in the engine pipe volume 85, downstream of the valve arrangement 19. The valve arrangement 19 is a two-block, bleed valve arrangement which receives the vapor flow from the supply pipe 18. The measured gas pressure is filtered in a filter 86.

[0071] The result of the comparison at the second summing point 76 is sent to the high pressure hydraulic fluid source 20. Based on that signal, the high pressure hydraulic fluid source 20 delivers hydraulic fluid having a modified pressure to the high pressure pump unit 40.

[0072] The electronic control unit 70 receives a signal indicative of the position of the drive piston and processes the position signal in a piston supervision unit 92. The piston supervision unit 92 is coupled to a piston actuation method unit 90. The operation details of the piston supervision unit 92 and the piston actuation method unit 90 are shown and described in further detail below. The piston actuation method unit 90 signal is sent to the control valve 24 of the high pressure pump 40 to actuate the drive piston 46.

[0073] Actuation of drive piston 46 pumps liquefied high pressure gas through high pressure vaporizer 14 and into supply line 18 .

[0074] The primary pressure control of the electronic control unit 70 is a feedforward: a PI (proportional integral) controller compensates for non-linearities and helps with transient variations.

[0075] The gas pressure is automatically controlled by setting the hydraulic feed pressure in the pump units 41, 42, 43. The pressure control is done on the hydraulic side and does not have to be on the gas side. If the hydraulic pressure is properly controlled, the gas pressure cannot become too high in this system.

[0076] The drive piston 46 is controlled via a control method that is not an active part of the pressure control.

[0077] Each pump unit 41, 42, 43 can be controlled separately. It is therefore possible to operate them in different piston ways and in various operating conditions. Furthermore, the possibility to operate the pump units 41, 42, 43 separately provides redundancy, since it is possible to change from three pump units 41, 42, 43 to two pump units between two strokes.

[0078] The return speed can be faster than the forward (pump) speed, which allows overlap when only two pump units are running. The overlap between pump units 41, 42, 43 can be adjusted according to the need to reduce pressure spikes.

[0079] To distribute wear over an area of ​​the pump cylinder 61, as opposed to high wear occurring at a fixed position on the cylinder, the end position of the pump stroke can change over time.

[0080] The system creates little or no overpressure even during sudden shutdown (piston stall) due to very low inertia and other factors that negatively affect dynamic response.

[0081] The control valve 24 can be a hydraulically controlled valve or an electronically controlled valve. In this embodiment where the control valve 24 is a hydraulically controlled valve, an electronically controlled solenoid valve (not shown) is provided to control the hydraulic control signal to the control valve 24. The electronically controlled solenoid valve receives an electronic control signal from an electronic control unit 70.

[0082] The electronic control unit 70, and in particular the piston actuation unit 90, is arranged to selectively connect the drive chambers 48 of the pump units 41, 42, 43 to the source 20 of high pressure hydraulic fluid or to a tank.

[0083] The electronic control unit 70, and in particular the piston actuation method unit 90, is configured to initiate a pump stroke of a drive piston 47 when a pump stroke of another drive piston 47 is nearing an end and there is a small overlap between the ending and starting pump strokes. In one embodiment, the electronic control unit 70 is configured to operate each drive cylinder substantially continuously, preferably with a small overlap. Thus, as illustrated in Figures 6 and 7, a substantially steady flow of LNG to the high pressure vaporizer 14 can be achieved without large pressure fluctuations.

[0084] Figures 6, 7 and 8 illustrate the normal operation of the high pressure pump 40. The light continuous line represents pump unit 41, the dark continuous line represents pump unit 42 and the dotted line represents pump unit 43. Figure 6 is a graph showing the movement of the drive piston 46 / pump piston 62. As can be seen from the graph, the pump stroke of the next pump unit starts just before the pump stroke of the currently operating pump unit ends. Figure 7 shows the resulting pressure composed of the pressure outputs from the transfer pipes 50 of the three pump units 41, 42, 43. The resulting pressure is substantially constant and does not fluctuate.

[0085] Figure 8 shows the speed profile of the pump units, where it can be clearly seen that the return stroke speed is significantly faster than the pump stroke speed, thus allowing for overlap between pump units even when using only two of three or more pump units.

[0086] In one embodiment, the electronic control unit 70, and more particularly the piston actuation method unit 90, is configured to take into account the power at the end of a pump stroke and the power at the beginning of a pump stroke in order to obtain a substantially constant flow of high pressure liquefied gas from the high pressure pump to the high pressure vaporizer 14.

[0087] In one embodiment, the electronic control unit 70, in particular the piston actuation method unit 90, is configured to determine when to start a pump stroke of one of the pump units 41, 42, 43 and to determine when to end a pump stroke of any of the drive units 41, 42, 43. Thus, the point at which a pump stroke starts, in particular the point at which a pump stroke ends, can be precisely controlled by the piston actuation method unit 90, preferably together with the piston supervision unit 92.

[0088] In one embodiment, the electronic control unit 70 is configured such that if one of the pump units 41, 42, 43 fails, the remaining functioning drive piston of the pump units 41, 42, 43 operates, thus providing redundancy and allowing pumping action to continue even if one of the pump units 41, 42, 43 fails.

[0089] In one embodiment, the electronic control unit 70 is configured to adjust the position of the drive piston 46 at which the drive chamber 48 is disconnected from the source of high pressure hydraulic fluid in relation to the magnitude of the flow of liquefied gas from the high pressure pump 40 to the high pressure vaporizer. Thus, the position at which the pump stroke reverses can be controlled regardless of the speed and resulting inertia of the drive piston 46 and pump piston 62.

[0090] According to one embodiment, when the flow of liquefied gas from the high pressure pump to the high pressure vaporizer increases, the electronic control unit 70 is configured to adjust the position of the drive piston 46 in the direction opposite to the drive stroke at a position where the drive chamber 48 of the associated drive piston 46 is disconnected from the source of high pressure liquid 20. Also, when the flow of liquefied gas from the high pressure pump to the high pressure vaporizer decreases, the electronic control unit 70 is configured to adjust the position of the drive piston 46 in the direction of the drive stroke at a position where the drive chamber 48 of the associated drive piston 46 is disconnected from the source of high pressure liquid 20. This is shown in Figures 10 and 11.

[0091] FIG. 10 shows the effect of increased speed of the drive piston 46 and pump piston 62 at the end of the drive / pump stroke. The light continuous line represents pump unit 41, the dark continuous line represents pump unit 42, and the dotted line represents pump unit 43. The electronic control unit 70 signals the hydraulic control valve 24 to connect the drive chamber 48 to the tank when the drive piston reaches 80 mm of stroke, regardless of the load / magnitude of the liquefied gas flow delivered by the high pressure pump 40. Due to inertia and higher speed, the stop / reverse position of the drive piston 46 changes from 85 mm at 25% load to 89 mm at 50% load to 98 mm at 100 percent load.

[0092] 11 is a graph showing the effect of the electronic control unit 70 compensating for the increased speed of the drive piston 46 / pump piston 62 by connecting the drive chamber 48 to the tank with a shorter stroke at high loads and a longer stroke at low loads. As can be seen in the graph, the electronic control unit 70 can thus precisely control the end position of the drive / pump stroke.

[0093] In the example graph, the signal to connect the drive chamber 48 to tank for a 25% load for the next drive cylinder (i.e., 25% of the maximum capacity of the high pressure pump 40) is issued when the previous cylinder is 75mm into the drive chamber. The drive chamber of the "previous" drive cylinder is connected to tank when that cylinder is 93mm into the drive chamber. The "signal ON" for the connection of the next drive cylinder to the high pressure source and the "signal OFF" for the connection of the "previous" cylinder to tank are shown in Table 1 below.

[0094] [Table 1]

[0095] Of course, it is also possible to program the electronic control unit 70 to intentionally vary the starting position in order to reduce wear on the pump cylinder 61.

[0096] In one embodiment, the electronic control unit 70 is configured to adjust the position of the drive piston 46 at which the drive chamber 48 of the associated drive piston 46 is disconnected from the source of high pressure fluid 20 by algorithm, schedule or randomly to distribute the positions at which the pump piston 62 reverses over the stroke area of ​​the pump piston 62 to reduce wear on the pump cylinder 61. It is known that wear on the pump cylinder 61 is most severe at the end of the pump stroke. By varying the end of the pump stroke, wear on the pump cylinder 61 can be spread over a larger area and therefore the life of the pump cylinder 61 can be significantly increased.

[0097] In one embodiment, the electronic control unit 70 is configured to control the activation and deactivation of each drive piston 46 independently of the control pressure of the hydraulic fluid supplied to the drive chamber 48. Thus, the control strategy for the actuation of the drive pistons can be optimized by the electronic control unit 70 independent of pressure control.

[0098] The present invention has been described with various embodiments herein. However, those skilled in the art who practice the claimed invention can understand and realize other variations of the disclosed embodiments by studying the drawings, the disclosure, and the appended claims. In the claims, the word "comprises" does not exclude other elements or steps, nor does it exclude that a configuration may be multiple if it is not specified that it may be multiple. An electronic control unit may be formed by a combination of individual electronic control units. The mere fact that certain measurements are recited in mutually different dependent claims does not indicate that a combination of these measurements cannot be used to advantage. Reference signs used in the claims should not be interpreted as limiting the scope.

Claims

1. A high-pressure pump for pressurizing liquefied gas, The high-pressure pump comprises two or more pump units, and each of the pump units is A pump cylinder, and a pump piston slidably disposed within the pump cylinder to form a pump chamber; With hydraulic linear actuators; Equipped with, The hydraulic linear actuator comprises a drive cylinder and a drive piston slidably disposed within the drive cylinder and mechanically connected to the pump piston to drive the pump piston. The two or more pump units are mechanically independent of each other. Each of the pump units can be individually controlled by controlling the working fluid supplied to each of the drive cylinders. High-pressure pump.

2. The high-pressure pump according to claim 1, wherein each of the two or more pump units comprises a hydraulic control valve configured to selectively connect the drive chamber of the drive cylinder to a source or tank for supplying high-pressure working fluid.

3. The high-pressure pump according to claim 1 or 2, wherein the drive piston divides the drive cylinder into a drive chamber and a return chamber.

4. A high-pressure pump according to any one of claims 1 to 3, comprising a controller configured to control the operation of the pump unit.

5. The high-pressure pump according to claim 4, wherein the controller is configured to control the operation of the two or more pump units such that when the pump stroke of one of the two or more pump units approaches its end, the pump stroke of another of the two or more pump units is initiated.

6. A system that supplies pressurized gas from liquefied gas, A high-pressure pump according to any one of claims 1 to 5; A control unit configured to control the pressure of the pressurized gas; A system comprising the control unit, wherein the control unit is configured to control the pressure of the pressurized gas by controlling the pressure of the working fluid supplied to the two or more pump units.

7. The system according to claim 6, wherein the control unit is configured to control the pressure of the working fluid based on a desired gas pressure.

8. The system according to claim 6 or 7, wherein the control unit includes a feedforward control function based on a desired gas pressure.

9. The system according to any one of claims 6 to 8, wherein the control unit includes a feedback control function based on the measured gas pressure.

10. The system according to any one of claims 6 to 9, wherein the control unit is configured to control the operation of the two or more pump units independently of the pressure control of the working fluid supplied to the two or more pump units.

11. A method for controlling the pressure of a gas supplied from a liquefied gas, Pressurizing the liquefied gas using a high-pressure pump having two or more hydraulically driven pump units; The pressure of the gas is controlled by controlling the pressure of the working fluid supplied to the two or more pump units; Methods that include...

12. The method according to claim 11, wherein the pressure of the working fluid is controlled based on a desired gas pressure.

13. The method according to claim 11 or 12, wherein the pressure of the working fluid is controlled based on the measured gas pressure.

14. A pump system for pressurizing liquefied gas, A pump comprising at least one pump unit having a pump piston configured to reciprocate within a pump cylinder; A controller configured to control the operation of the pump piston; A pump system comprising the controller configured to control the position where the pump stroke of the pump piston ends.

15. The pump system according to claim 14, wherein the controller is configured to control the position according to the flow rate of the liquefied gas supplied by the pump.

16. The pump system according to claim 14 or 15, wherein the controller is configured to control the position according to the operating load of the pump.

17. The pump system according to claim 15, wherein the controller is configured to terminate the pump stroke at an earlier position when the flow rate increases.

18. The pump system according to claim 15, wherein the controller is configured to terminate the pump stroke at a later position when the flow rate decreases.

19. The pump system according to claim 14, wherein the controller is configured to change the position where the pump stroke ends over time so as to distribute wear over the entire stroke range of the pump piston.

20. The pump system according to claim 19, wherein the controller is configured to change the position according to an algorithm.

21. The pump system according to claim 19, wherein the controller is configured to change its position according to a predetermined plan.

22. The pump system according to claim 19, wherein the controller is configured to randomly change the position.

23. The pump system according to claim 14, wherein the controller is configured to control the position in accordance with the dynamic behavior of the pump piston.

24. The pump system according to claim 23, wherein the dynamic behavior includes the inertia of the pump piston.

25. The pump system according to claim 14, wherein the pump has a plurality of pump units, and the controller is configured to coordinate the operation of the plurality of pump units.

26. The pump system according to claim 25, wherein the controller is configured to start the pump stroke of another of the plurality of pump units when the pump stroke of one of the plurality of pump units approaches its end.

27. A method for operating a pump to pressurize liquefied gas, The reciprocating motion of the pump piston within the pump cylinder; Controlling the position where the pump stroke of the pump piston ends; Methods that include...

28. The method according to claim 27, wherein the position is controlled according to the flow rate of liquefied gas supplied by the pump.

29. The method according to claim 27 or 28, wherein the position is changed over time in order to distribute wear over the entire stroke range of the pump piston.

30. The method according to claim 29, wherein the position is changed by an algorithm, a predetermined plan, or randomly.

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